This invention relates to an apparatus for influencing the flow of air through a passageway and more specifically, but not exclusively, to an apparatus for providing thrust reversal for a turbine engine.
Most fixed-wing airplanes have high landing speeds, which result in a large burden being placed on the wheel brakes. To reduce this burden, most jet airplanes, that is, airplanes that have gas turbine propulsion units, are equipped with thrust reversers which provide a reversed flow of air. In a gas turbine propulsion unit, in which a nacelle surrounds the engine and is spaced outwardly from the engine cowl to define an annular passageway for the flow of air downstream from the engine fan, a large proportion of the total thrust is developed by the reaction to the air driven through the passageway by the fan. In such a propulsion unit, reverse thrust may be provided by blocking the downstream flow of air through the passageway and diverting it laterally and forwardly by employing a combination of blocker doors.
FIG. 1 is a cross-sectional view of a typical gas turbine propulsion unit 2. Propulsion unit 2 comprises an engine 4 composed of a combustor and turbine (not shown), a compressor 6 and a fan 8. The combustor, turbine and compressor are enclosed by an engine cowl 10, and the fan is enclosed by a fan cowl 16, constituted by the inner wall of a double-walled nacelle 24. An exhaust nozzle 20 is attached to the downstream end of engine 10 to exhaust gases from the engine into the atmosphere. An inner cowl 12 is attached to and supported by the inner wall of the nacelle and covers the engine cowl 10 and engine accessories. When the engine is in use, fan 8 is driven to rotate within fan cowl 16, creating a flow of air to the right of FIG. 1. Part of the flow enters compressor 6 and is delivered to the combustor to support the combustion of fuel, and the rest of the flow passes through a smooth-walled annular passageway, defined between the inner cowl 12 and a double-walled outer cowl 22 that forms part of the nacelle. The flow through annular passageway 26 passes out the rear of the propulsion unit through an annular exit nozzle 28. The nacelle extends forward of fan cowl 16 in the form of an inlet cowl to provide smooth flow surfaces into and around the nacelle.
FIGS. 2A and 2B illustrate a portion of a nacelle 30 incorporating a thrust reverser of known construction in a forward thrust configuration and a reverse thrust configuration respectively. The thrust reverser is positioned in a translating sleeve 32, the aft portion of which forms the outer wall of the nozzle 28. A blocker door 34 is attached to the inner cowl 12 by a linkage 36 and to the translating sleeve by a pinned joint 38. The translating sleeve is attached to the structure of the nacelle by actuators 40. A "bullnose" 42 having a convex curvature is positioned upstream of the sleeve 32 adjacent passageway 26 for assisting to turn the flow of air when the apparatus is in the reverse thrust configuration. A plurality of nozzle vents 44 (cascades) to turn the flow are positioned downstream of the bullnose within the translating sleeve.
In the forward thrust configuration shown in FIG. 2A, the blocker door 34 forms part of the inner wall of the nacelle, allowing air flow through the passageway 26 and out of the nozzle 28. In the reverse thrust configuration shown in FIG. 2B, the actuators 40 have translated the sleeve 32 aft, whereby blocker door 34 has pivoted into passageway 26 such that the flow of air is diverted through the nozzle vents 44 in a substantially reverse direction. Translating the sleeve aft opens a gap in the outer wall of the nacelle adjacent the cascades allowing the air to flow from the passageway through the cascades and out into the atmosphere.
In U.S. Pat. No. 3,475,913, Mortlock et al disclose a thrust reverser for a gas turbine engine in which inner and outer doors are pinned at their aft ends and are linked to a ring which is slidably mounted on tracks within a double outer wall of the nacelle and positioned by an actuator. In a first position, the doors are recessed into the walls of the nacelle and form a portion of the wall. In a second position, the doors have swung open, one blocking the rearward flow of air from the fan and the other directing the air in a reverse direction outside the nacelle.
In U.S. Pat. No. 3,483,702, Ward discloses a thrust reverser for a gas turbine engine comprising two doors, a first door pinned at its aft end and linked to a ram slidably mounted on tracks within a double wall of the nacelle and a second door pinned to the first door and to a pivot enclosed in a cam slot. A cascade of vents is positioned in the double wall between the two doors. In a first position, the doors form part of the inner and outer walls respectively of the nacelle and in a second position the first door has swung into the passage to divert the flow of air through the cascade. The second door is positioned outwardly to direct the flow of air in a reverse direction.
In U.S. Pat. No. 3,605,411, Maison et al disclose a thrust reverser comprising two doors positioned in a double-walled nacelle spaced outwardly from an engine cowl to define an annular duct. The doors are pinned to the cowl separately and to each other through a link. The outer door is linked to an actuator. In a first position, the doors form a portion of the wall allowing air to flow through the duct. In a second position, one door has pivoted into the duct blocking the flow of air. The other door is positioned outwardly to influence the air flow in a reverse direction.
In U.S. Pat. No. 3,690,561, Potter describes a thrust controlling system wherein a nozzle slides rearward thus exposing openings in an air duct and causing two doors to pivot, one blocking the flow of air through the duct and the other directing the air to provide reverse thrust.